Process for the preparation of isoolefin copolymers

ABSTRACT

The present invention provides a novel process for the preparation of isoolefin copolymers in the presence of zirconium halides or hafnium halides or mixtures thereof and organic nitro compounds, especially for the preparation of butyl rubbers, as well as isoolefin copolymers composed of isobutene, isoprene and, optionally, further monomers.

This is a divisional of U.S. patent application Ser. No. 09/941,176filed on Aug. 27, 2001 now U.S. Pat. No. 6,562,916.

FIELD OF THE INVENTION

The present invention provides a novel process for the preparation ofisoolefin copolymers in the presence of zirconium halides and/or hafniumhalides and organic nitro compounds, especially for the preparation ofbutyl rubbers having a relatively high isoprene content, as well asisoolefin copolymers composed of isobutene, isoprene and, optionally,further monomers.

BACKGROUND OF THE INVENTION

Presently, the process used for producing butyl rubber is known, forexample, from Ullmanns Encyclopedia of Industrial Chemistry, Vol. A 23,1993, pages 288-295. The cationic copolymerization of isobutene withisoprene by the slurry process and with methylene chloride as theprocess solvent is carried out using aluminum trichloride as initiatorwith the addition of small amounts of water or hydrogen chloride at −90°C. The low polymerization temperatures are necessary in order to achievesufficiently high molecular weights for rubber applications.

The molecular-weight-lowering (=regulating) effect of the dieniccomonomers can, in principle, be compensated for by even lower reactiontemperatures. In such a case, however, the side-reactions that lead togel formation occur to a greater extent. Gel formation at reactiontemperatures of about −120° C. and possible methods for the reductionthereof have been described (see: W. A. Thaler, D. J. Buckley, Sr.,Meeting of the Rubber Division, ACS, Cleveland, Ohio, May 6-9, 1975,published in Rubber Chemistry & Technology 49, 960-966 (1976)). Theauxiliary solvents, such as CS₂, that are necessary therefor are on theone hand difficult to handle and, in addition, must be used inrelatively high concentrations.

Also known is the gel-free copolymerization of isobutene with variouscomonomers at temperatures of about −40° C. using pre-formed vanadiumtetrachloride, to form products having a sufficiently high molecularweight for rubber applications (EP-A1-818 476).

U.S. Pat. No. 2,682,531 describes zirconium tetrachloride-ethercomplexes and the use thereof as catalysts for the polymerization of,inter alia, isoolefins. In column 2, line 20 et seq, it is emphasizedthat the use of zirconium tetrachloride alone leads to unsatisfactoryresults. The ether that is preferably used is β,β′-dichloroethyl ether,which is carcinogenic. Diphenyl ether, which is also mentioned as anexample, leads only to poorly soluble complexes that exhibit adequateactivity only when metered in extremely large amounts. Diethyl ether(which is mentioned specifically as a possible ether in the patent)leads to complexes that are completely inactive.

SUMMARY OF THE INVENTION

The object of the present invention was to provide a process for thepreparation of high molecular weight, low-gel isoolefin copolymers,especially for the preparation of butyl rubbers having more than 2%isoprene in the polymer.

The present invention provides a process for the preparation of highmolecular weight isoolefin copolymers in the presence of zirconiumhalides and/or hafnium halides, wherein the process comprises the stepof carrying out polymerization in the presence of organic nitrocompounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the molecular weight distribution of Example 2.

FIG. 2 shows Mv as a function of temperature, the parameters of thecurve are y=2E−05×^(14.133)R²=0.9559.

DETAILED DESCRIPTION OF THE INVENTION

The process is preferably used in the case of isoolefins having from 4to 16 carbon atoms and dienes that are copolymerizable with theisoolefins optionally in the presence of further monomers that arecopolymerizable with the monomers. Special preference is given to theuse of isobutene and isoprene optionally in the presence of furthermonomers that are copolymerizable therewith.

The process is preferably carried out in a solvent suitable for cationicpolymerization, such as halogenated and non-halogenated hydrocarbons ormixtures thereof, especially chloroalkanes and chloroalkane/alkanemixtures, preferably methyl chloride and methylene chloride or mixturesthereof with alkanes.

The zirconium halide and/or hafnium halide is preferably mixed with thenitroorganic compound in the absence of the monomer.

The organic nitro compounds that are used are generally known andgenerally available. The nitro compounds that are preferably usedaccording to the present invention are defined by the general formula(I)R—NO₂  (I)wherein R is selected from the group C₁-C₁₈-alkyl, C₃-C₁₈-cycloalkyl orC₆-C₂₄-cycloaryl.

C₁-C₁₈-Alkyl is to be understood as meaning all linear or branched alkylradicals having from 1 to 18 carbon atoms that are known to the personskilled in the art, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl and thefurther homologues, which in turn may be substituted. Suitablesubstituents are especially alkyl, as well as cycloalkyl or aryl, suchas benzyl, trimethylphenyl, ethylphenyl. Linear alkyl radicals havingfrom 1 to 18 carbon atoms are preferred, especially methyl, ethyl andbenzyl.

C₆-C₂₄-Aryl is to be understood as meaning all mono- or poly-nucleararyl radicals having from 6 to 24 carbon atoms that are known to theperson skilled in the art, such as phenyl, naphthyl, anthracenyl,phenanthracenyl and fluorenyl, which, in turn, may be substituted.Suitable substituents are especially alkyl, as well as cycloalkyl oraryl, such as toloyl and methylfluorenyl. Phenyl is preferred.

C₃-C₁₈-Cycloalkyl is to be understood as meaning all mono- orpoly-nuclear cycloalkyl radicals having from 3 to 18 carbon atoms thatare known to the person skilled in the art, such as cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and thefurther homologues, which, in turn, may be substituted. Suitablesubstituents are especially alkyl, as well as cycloalkyl or aryl, suchas benzyl, trimethylphenyl, ethylphenyl. Cyclohexyl and cyclopentyl arepreferred.

The concentration of the organic nitro compound in the reaction mediumis preferably in the range from 5 to 15,000 ppm, especially in the rangefrom 50 to 7000 ppm. The molar ratio of nitro compound to zirconiumand/or hafnium is preferably in the region of 100:1, more preferably, inthe region of 25:1 and most preferably, in the range from 14:1 to 1:1.

Polymerization of the monomers is generally carried out cationically attemperatures in the range from −120° C. to +20° C., preferably in therange from −100° C. to −20° C., and at pressures in the range from 0.1to 4 bar.

Suitable zirconium halides and/or hafnium halides are, for example,zirconium dichloride, zirconium trichloride, zirconium tetrachloride,zirconium oxydichloride, zirconium tetrafluoride, zirconium tetrabromideand zirconium tetraiodide, hafnium dichloride, hafnium trichloride,hafnium oxydichloride, hafnium tetrafluoride, hafnium tetrabromide andhafnium tetraiodide and hafnium tetrachloride. Zirconium halides and/orhafnium halides having sterically demanding substituents, such as, forexample, zirconocene dichloride or bis(methylcyclopentadienyl)zirconiumdichloride, are generally unsuitable. Preference is given to the use ofzirconium tetra-chloride. It may advantageously be used in the form of asolution in an anhydrous and oxygen-free alkane or chloroalkane, or amixture of the two, having a zirconium concentration of less than 4 wt.%. It may be advantageous to store (age) the Zr solution for a period offrom a few minutes up to 1000 hours at room temperature or below beforeit is used. It may be advantageous to carry out such aging under theaction of light.

It may also be advantageous to use mixtures of the catalyst systemaccording to the present invention with conventional catalysts, such asAlCl₃ and catalyst systems that can be prepared from AlCl₃,diethylaluminum chloride, ethylaluminum chloride, titaniumtetrachloride, tin tetrachloride, boron trifluoride, boron trichloride,vanadium tetrachloride or methylalumoxane, especially AlCl₃ and catalystsystems that can be prepared from AlCl₃. Such a combination forms afurther subject of the invention.

In the preparation of such mixtures, the molar ratio Lewisacid:zirconium and/or hafnium may be in the range from 99:1 to 1:99,preferably in the range from 99:1 to 1:1, more preferably in the rangefrom 20:1 to 5:1.

The molar ratio of nitro compound to zirconium and/or hafnium in suchmixtures is preferably in the region of 1000:1, more preferably in theregion of 250:1 and most preferably in the range from 100:1 to 1:1.

It may be advantageous to add to the catalyst system small amounts ofwater, alcohols, of an alkyl halide or hydrogen halide.

The polymerization may be carried out in either continuous ordiscontinuous operation. In the case of continuous operation, theprocess is preferably carried out with the following three feed streams:

-   solvent/diluent+isoolefin (preferably isobutene)-   diene (preferably isoprene)-   zirconium halide and/or hafnium halide (preferably ZrCl₄ in    solvent)+organic nitro compound.

In the case of discontinuous operation, the process may be carried out,for example, as follows:

The reactor, pre-cooled to reaction temperature, is charged with thesolvent or diluent and the monomers. The initiator together with thenitro compound in the form of a dilute solution is then pumped in, suchthat the heat of polymerization can be dissipated without difficulty.The progress of the reaction can be monitored by means of the evolutionof heat.

All operations are carried out under protecting gas. When thepolymerization is complete, the reaction is terminated using a phenolicantioxidant, such as, for example,2,2′-methylene-bis-(4-methyl-6-tert-butylphenol), dissolved in ethanol.

By means of the process according to the present invention it ispossible to prepare high molecular weight isoolefin copolymers. Thedouble bonds are determined by the amount of diene that is incorporated.The molecular weights (Mv) usually range (according to the isoprenecontent and the reaction temperature) from 300 to 1200 kg/mol, and thepolymers have a very low gel content.

A major advantage of the process according to the present invention is,in addition, the marked reduction in so-called “fouling”. The personskilled in the art will understand by fouling the formation of polymerdeposits on the walls of the reactor and inside the heat exchanger. As aresult of such deposits, dissipation of the heat of reaction that formsis impaired and, ultimately, disrupted to such an extent that thereactor must be cleaned after a few days in order to ensure properoperation.

The polymers that are obtainable are surprisingly well suited for theproduction of molded bodies of any kind, especially tire components,very especially so-called inner liners, as well as so-called technicalrubber articles, such as plugs, damping elements, profile sections,films, coatings. To that end, the polymers are used in pure form or inadmixture with other rubbers, such as BR, HNBR, NBR, SBR, EPDM orfluorine rubbers.

The Examples which follow are given to illustrate the present invention:

EXAMPLES

Experimental Details

The gel contents were determined in toluene after a dissolving time of24 hours at 30° C. with a sample concentration of 12.5 g/l. Theinsoluble constituents were separated off by ultracentrifugation (1 hourat 20,000 rpm and 25° C.). Samples having a high gel content wereexamined in o-dichlorobenzene at 140° C.

The intrinsic viscosity η of the soluble constituents was determined intoluene at 30° C. by Ubbelohde capillary viscometry.

The molecular weight Mv calculated from the limiting viscosity numberwas determined according to the following formula: In(M_(v))=12.48+1.565*In η.

The Mooney value was determined at 125° C. after a measurement time of 8minutes.

The protecting gas used was argon of grade 4.8 (Linde).

The monomer incorporation and the branching point¹ were determined bymeans of high-field proton resonance.

The isobutene (Gerling+Holz, Germany, grade 2.8) used in thepolymerizations was, for drying purposes, passed through a column packedwith sodium on aluminum oxide (content 10%).

In order to remove the stabilizer, the isoprene (Acros, 99%) that wasused was filtered under argon through a column of dried aluminum oxide,distilled over calcium hydride under an argon atmosphere, and used inthat form for the polymerization. The water content was 25 ppm.

The methyl chloride (Linde, grade 2.8) that was used was, forpurification purposes, passed through a column of activated carbon andthrough a further column containing Sicapent, and was used in that form.

The methylene chloride (Merck, grade: for analysis ACS, ISO) wasdistilled over phosphorus pentoxide, under an argon atmosphere, fordrying purposes.

The nitromethane (Aldrich, 96%) was first stirred for two hours withphosphorus pentoxide, a constant stream of argon being passed throughthe mixture. Distillation was then carried out in vacuo at about 20mbar.

The zirconium tetrachloride (>=98%) that was used was obtained fromFluka.

The aluminum trichloride (98.5%) that was used was obtained from JanssenChimica.

A prechilled solution of 2 g Irganox 1010 (Ciba) in 250 ml of ethanolwas used to terminate the polymerization reactions.

Example 1 (Preparation of the Initiator)

14.56 g (62.5 mmol) of zirconium tetrachloride were placed in atwo-necked round-bottomed flask under an argon atmosphere. 500 ml ofmethylene chloride and 44.3 ml (49.9 g) of nitromethane were added(ratio Zr/nitromethane 1:13).

The mixture was stirred for 2 hours at room temperature and then left tostand for 24 hours. The still undissolved constituents (small amount,presumably zirconium dioxide) settled at the bottom of the flask duringthat time. The colorless supernatant solution was used to initiate thepolymerization.

In the course of several days, a change in the color of the solution toyellow→orange is observed, obviously as a result of decomposition of theinitiator. A slight yellow coloring can be tolerated, an orange-coloredsolution loses a large part of its activity.

Example 2

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 52 g (0.93 mol) of isobutene were condensed (concentration 6.91 wt.%) under an argon atmosphere at a temperature of −80° C.

After addition of 1.6 g (0.02 mol, 2.35 ml) of isoprene (2.47 mol %), 3ml of initiator solution from Example 1 were metered in during thecourse of 5 minutes. The vigorous reaction was terminated after 5minutes. A finely divided milky suspension was obtained, without theformation of flakes and without fouling.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 1 below.

TABLE 1 Yield 22.5 g (42%) Staudinger index 1.096 dl/g Molecular weightMv 303.6 kg/mol Mn 185.1 kg/mol Mw 436.5 kg/mol Gel content 0.7%Isoprene incorporation 2.2%FIG. 1 Shows the Result of the GPC Investigation of Example 2.

Example 3

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 25 ml of initiatorsolution according to Example 1 were metered in during the course of 30minutes. A milky suspension was obtained, fouling did not occur. Theweak reaction was terminated after 30 minutes.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 2 below.

TABLE 2 Yield 42.1 g (33.7%) Staudinger index 1.74 dl/g Gel content 0.6%Molecular weight Mv 625.8 kg/mol Mn 386.2 kg/mol Mw 830.1 kg/molIsoprene incorporation 1.9% Mooney value 81.5

Example 4

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 300 g (5.35 mol) of isobutene were condensed (concentration 30 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 27.4 g (0.4 mol, 40.23 ml) of isoprene (7 mol %), 7 ml of initiatorsolution according to Example 1 were metered in during the course of 10minutes. The vigorous reaction was terminated after 5 minutes.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 3 below.

TABLE 3 Yield 12.1 g (3.7%) Staudinger index 2.337 dl/g Molecular weightMv 993 kg/mol Mn 448.8 kg/mol Mw 1070 kg/mol Gel content 1.5% Isopreneincorporation 3.5%

Example 5 (Comparison Example According to U.S. Pat. No. 2,682,531:Preparation of the Initiator)

14.56 g (62.5 mmol) of zirconium tetrachloride were placed in a 33methylene chloride and 10.5 ml (11.3 g) of diphenyl ether were added(ratio Zr/diphenyl ether 1:1).

The mixture was stirred for 6 hours at room temperature and then left tostand for 22 days. The still undissolved constituents settled at thebottom of the flask during that time. The deep-red supernatant solutionwas used to initiate the polymerization.

Example 6 (Comparison Example According to U.S. Pat. No. 2,682,531:Polymerization)

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 230 g (4.10 mol) of isobutene were condensed (concentration 26.4 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 21 g (0.31 mol, 30.84 ml) of isoprene (7 mol %), 150 ml of initiatorsolution (Example 5) were metered in during the course of 45 minutes.The reaction was terminated immediately after the addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 4 below.

TABLE 4 Yield 125.8 g (50.12%) Staudinger index 0.919 dl/g Molecularweight Mv 230.4 kg/mol Mn 54.9 kg/mol Mw 370.6 kg/mol Gel content 29%Mooney value 44.3

The analytical results for the product show only a low molecular weight,despite the good Mooney value, and a gel content that is much too highfor most rubber applications. Example 4 according to the presentinvention, which was carried out under comparable conditions, resultedin a markedly better product.

Preparation of further initiator systems using various nitro compounds

Example 7 (Preparation of an Initiator Using 2-nitropropane)

11.4 g (48.9 mmol) of zirconium tetrachloride were placed in atwo-necked round-bottomed flask under an argon atmosphere. 390 ml ofmethylene chloride and 95 ml (94.24 g) of 2-nitropropane were added(ratio Zr/nitro compound 1:21.6).

The mixture was stirred for 2 hours at room temperature and then left tostand for 5 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 8 (Preparation of an Initiator using 1-nitropropane)

0.7 g (3 mmol) of zirconium tetrachloride was placed in a two-neckedround-bottomed flask under an argon atmosphere. 24 ml of methylenechloride and 3.5 ml (3.47 g) of 1-nitropropane were added (ratioZr/nitro compound 1:13).

The mixture was stirred for 2 hours at room temperature and then left tostand for 2 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 9 (Preparation of an Initiator using Nitroethane)

1.9 g (8.15 mmol) of zirconium tetrachloride were placed in a two-neckedround-bottomed flask under an argon atmosphere. 65 ml of methylenechloride and 7.8 ml (8.15 g) of nitroethane were added (ratio Zr/nitrocompound 1:13.3).

The mixture was stirred for 2 hours at room temperature and then left tostand for 4 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 10 (Preparation of an Initiator using Nitrobenzene)

9.7 g (41.6 mmol) of zirconium tetrachloride were placed in a two-neckedround-bottomed flask under an argon atmosphere. 330 ml of methylenechloride and 60 ml (71.76 g) of nitrobenzene were added (ratio Zr/nitrocompound 1:14).

The mixture was stirred for 2 hours at room temperature and then left tostand for one day. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Use of the initiator systems of Examples 7 to 10

Example 11

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 25 ml of initiatorsolution according to Example 7 were metered in during the course of 30minutes. The weak reaction was terminated after 30 minutes.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 5 below.

TABLE 5 Yield 1.1 g (0.9%) Staudinger index 0.682 dl/g Gel content 1.1%Molecular weight Mv 144.5 kg/mol Mn 82.6 kg/mol Mw 198.3 kg/mol

The analytical results show that 2-nitropropane in the form of thebranched compound has markedly poorer properties than linearnitro-alkyls.

Example 12

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 5 ml of initiatorsolution according to Example 8 were metered in during the course of 5minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The vigorous reaction was terminated immediately afterthe addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 6 below.

TABLE 6 Yield 4.1 g (3.3%) Staudinger index 2.2 dl/g Gel content 0.9%Molecular weight Mv 903.4 kg/mol Mn 610.2 kg/mol Mw 1294 kg/mol

Example 13

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 6 ml of initiatorsolution according to Example 9 were metered in during the course of 10minutes. A milky suspension was obtained, fouling did not occur. Thevigorous reaction was terminated immediately after the addition wascomplete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 7 below.

TABLE 7 Yield 6.4 g (5.1%) Staudinger index 1.451 dl/g Gel content 0.8%Molecular weight Mv 471 kg/mol Mn 304.1 kg/mol Mw 627.9 kg/mol

Example 14

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 25 ml of initiatorsolution according to Example 10 were metered in during the course of 30minutes. The weak reaction was terminated after 30 minutes.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 8 below.

TABLE 8 Yield 2.3 g (0.9%) Staudinger index 1.721 dl/g Gel content 1.2%Molecular weight Mv 615.2 kg/mol Mn 363.9 kg/mol Mw 877.7 kg/mol

Example 15 Dependence of the Molecular Weights on Temperature GeneralProcedure

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 52 g (0.93 mol) of isobutene were condensed (concentration 6.9 wt.%) under an argon atmosphere at a temperature of −70° C. After additionof 1.6 g (0.02 mol, 2.4 ml) of isoprene (2.47 mol %), the batch wasbrought to the desired reaction temperature by heating or by cooling,and the initiator solution according to Example 1 was metered in. Thegenerally very vigorous reaction was terminated as soon as it was nolonger possible to control the temperature.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The details of the individual tests are shown in Table 9 below.

TABLE 9 Reaction Staudinger ml of Reaction temperature index initiatortime No (° C.) (dl/g) T (K) 1/T*1000 Mv (g/mol) solution (min) Yield (g)a −95 1.925 178.16 5.6129322 733042.632 5 1 6.8 b −85 1.924 188.165.31462585 732446.765 5 1 12.3 c −80 1.096 193.16 5.17705529 303597.8223 5 22.5 d −70 0.693 203.16 4.92222879 148163.984 9 15 25.2 e −60 0.348213.16 4.69131169 50415.7986 4 10 23 f −50 0.308 223.16 4.481089841646.3558 4 10 26.4 g −40 0.219 233.16 4.28890033 24422.5031 7 10 36.4The dependence of the molecular weight on temperature is shown in FIG.2.

Example 16 (Variation of the Amount of Isoprene) General Procedure

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 52 g (0.93 mol) of isobutene were condensed (concentration 6.9 wt.%) under an argon atmosphere at a temperature of −80° C. After additionof different amounts of isoprene, the initiator solution according toExample 1 was metered in. The generally very vigorous reaction wasterminated as soon as it was no longer possible to control thetemperature.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The details of the individual tests are shown in Table 10 belo

TABLE 10 Initiator Staudinger Gel Total isoprene 1,4-isoprene IsopreneIsoprene solution Yield index content incorporation, incorporation, No(g) (mol %) (ml) (g) (dl/g) (wt. %) Mv (g/mol) mol % mol % a 0 0.000 37.6 3.348 1 1,742,948 0 b 1 1.559 4 10.2 1.488 0.9 489,913 0.8 0.7 c1.16 1.804 6 18.1 1.553 0.8 523,816 0.9 0.83 d 1.3 2.018 5 11.2 1.5190.8 505,980 1 0.91 e 4 5.959 7 20.3 0.98 0.4 254,838 2.9 2.42 f 7 9.98114 25.6 0.914 0.7 228,495 6 5.01 g 15.8 20.018 11 12.0 0.968 1.2 249,97111.2 9.31As will be seen from this Table, virtually gel-free copolymers ofisobutene and isoprene having an isoprene content of more than 10% canbe prepared at −80° C. using the initiator system according to thepresent invention.

Combinations of zirconium tetrachloride with Lewis acids

Example 17 AlCl₃/ZrCl₄ 9:1

1.2 g (5.1 mmol) of zirconium tetrachloride and 6.2 g (46.5 mmol) ofaluminum trichloride were placed in a two-necked round-bottomed flaskunder an argon atmosphere. 410 ml of methylene chloride and 23 ml (25.9g) of nitromethane were added (ratio Zr/nitro compound 1:82.5).

The mixture was stirred for 2 hours at room temperature and then left tostand for 5 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 18 AlCl₃/ZrCl₄ 19:1

0.7 g (3.0 mmol) of zirconium tetrachloride and 7.6 g (57.0 mmol) ofaluminum trichloride were placed in a two-necked round-bottomed flaskunder an argon atmosphere. 480 ml of methylene chloride and 3 ml (3.38g) of nitromethane were added (ratio Zr/nitro compound 1:18.4).

The mixture was stirred for 2 hours at room temperature and then left tostand for 2 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 19 TiCl₄/ZrCl₄ 9:1

1.4 g (6.0 mmol) of zirconium tetrachloride and 10.207 g (53.8 mmol) oftitanium tetrachloride were placed in a two-necked round-bottomed flaskunder an argon atmosphere. 480 ml of methylene chloride and 7 ml (7.89g) of nitromethane were added (ratio Zr/nitro compound 1:21.5).

The mixture was stirred for 2 hours at room temperature and then left tostand for 4 days. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 20 AlCl₃/ZrCl₄ 9:1 with Activation by Means of HCl

12.2 g (52.4 mmol) of zirconium tetrachloride were placed in atwo-necked round-bottomed flask under an argon atmosphere. 420 ml ofmethylene chloride and 35 ml (39.4 g) of nitromethane were added (ratioZr/nitro compound 1:12.3).

The mixture was stirred for 2 hours at room temperature and then left tostand for one day. A slow stream of HCl was then passed through thesolution for 10 minutes. The solution turned yellow in color during thattime. When the still undissolved constituents (small amount) hadsettled, the supernatant solution was used to initiate thepolymerization.

Use of the initiator systems of Examples 17 to 20

Example 21

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 25 ml of initiatorsolution according to Example 17 were metered in during the course of 30minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The weak reaction was terminated after 30 minutes.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 11 below.

TABLE 11 Yield 7.5 g (6%) Staudinger index 1.334 dl/g Gel content 1.8%Molecular weight Mv 412.9 kg/mol Mn 279.3 kg/mol Mw 563.4 kg/mol

Example 22

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 15 ml of initiatorsolution according to Example 18 were metered in during the course of 20minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The vigorous reaction was terminated immediately afterthe addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 12 below.

TABLE 12 Yield 20.7 g (16.5%) Staudinger index 1.489 dl/g Gel content0.5% Molecular weight Mv 607.7 kg/mol Mn 336.4 kg/mol Mw 685.1 kg/mol

Example 23

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 66 ml of initiatorsolution according to Example 19 were metered in during the course of 70minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The vigorous reaction was terminated immediately afterthe addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 13 below.

TABLE 13 Yield 49.1 g (39.3%) Staudinger index 1.46 dl/g Gel content0.4% Molecular weight Mv 475.6 kg/mol Mooney value 76

Example 24

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 6 ml of initiatorsolution according to Example 20 were metered in during the course of 5minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The vigorous reaction was terminated immediately afterthe addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 14 below.

TABLE 14 Yield 12.2 g (9.8%) Staudinger index 2.079 dl/g Gel content0.2% Molecular weight Mv 826.9 kg/mol

Example 25 Hafnium tetrachloride/nitromethane

17.9 g (55.9 mmol) of hafnium tetrachloride were placed in a two-neckedround-bottomed flask under an argon atmosphere. 450 ml of methylenechloride and 32 ml (36.1 g) of nitromethane were added (ratio Hf/nitrocompound 1:10.6).

The mixture was stirred for 2 hours at room temperature and then left tostand for one day. The still undissolved constituents (small amount)settled at the bottom of the flask during that time. The colorlesssupernatant solution was used to initiate the polymerization.

Example 26

In a two-liter four-necked flask, 700 g (679.2 ml) of methyl chlorideand 120 g (2.14 mol) of isobutene were condensed (concentration 15 wt.%) under an argon atmosphere at a temperature of −95° C. After additionof 4.98 g (0.07 mol, 7.3 ml) of isoprene (3.3 mol %), 11 ml of initiatorsolution according to Example 25 were metered in during the course of 15minutes. A milky suspension with occasional flocks was obtained, foulingdid not occur. The vigorous reaction was terminated immediately afterthe addition was complete.

The polymer that formed was precipitated by addition of 2500 ml ofacetone, pre-dried by pressing on a laboratory roll and then driedovernight in vacuo at 50° C.

The analytical results are shown in Table 15 below.

TABLE 15 Yield 21 g (16.8%) Staudinger index 2.427 dl/g Gel content 0.4%Molecular weight Mv 1053 kg/mol

FIG. 1 shows the molecular weight distribution of Example 2.

FIG. 2 shows Mv as a function of temperature, the parameters of thecurve are y=2E−05×^(14.133) R²=0.9559.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A mixture comprising zirconium halides or hafnium halides or mixturesthereof and an organic nitro compound of the general formula (I)R—NO₂  (I) wherein R is selected from the group C₁-C₁₈-alkyl,C₃-C₁₈-cycloalkyl or C₆-C₂₄-cycloaryl.
 2. A catalyst comprising amixture of zirconium halides or hafnium halides or mixtures thereof andan organic nitro compound of the general formula (I)R—NO₂  (I) wherein R is selected from the group C₁-C₁₈-alkyl,C₃-C₁₈-cycloalkyl or C₆-C₂₄-cycloaryl.
 3. A polymer produced by aprocess comprising the steps of preparing isoolefin copolymers in thepresence of zirconium halides or hafnium halides or mixtures thereof andcarrying out the polymerization in the presence of organic nitrocompounds.
 4. A polymer according to claim 3, wherein said mixturecomprises up to 30 mol % isoprene.
 5. A molded body comprising a polymerproduced by a process comprising the steps of preparing isoolefincopolymers in the presence of zirconium halides or hafnium halides ormixtures thereof and carrying out the polymerization in the presence oforganic nitro compounds.